Knot-tying mechanism for sewing machine



Nov. 1s, 1969 K. HERMANN 3,478,708

KNOTJIYING MECHANISM FOR SEWTNG MACHINE Filed Oct. 16, 1967 2 Sheets-Sheet l HWUR ART INVENTOR:

ATTORNEK KURTEMEMANN NOV. 18,1969 K, B|ERMANN 3,478,708

KIIIOT-TYING MECHANISM FOR SEWING MACHINE Filed Oct. 16, 1967 2 Sheets-Shee'rl 2 Kur Biermann INVENTOR.

aw x9' L Attorney AUnited States Patent O 3,478,708 KNOT-TYING MECHA'NISM FOR SEWING MACHINE Kurt Biermann, Brake, near Bielefeld, Germany, assignor to Durkopp Aktiengesellschaft, Bielefeld, Germany, a corporation of Germany Continuation-in-part of application Ser. No. 513,931,

Dec. 15, 1965. This application Oct. 16, 1967, Ser. No. 675,638 Claims priority, application Germany, Dec. 15, 1964, D 46 066 Int. c1. Dosb 3/54; Bssh 69/04 U.S. Cl. 112-160 3 Claims ABSTRACT OF THE DISCLOSURE This application is a continuation-in-part of my copeuding application Ser. No. 513,931 tiled Dec. 15, 1965 and now abandoned.

My present invention relates to a mechanism for tying knots between a needle thread and an underthread in the operation of a sewing machine.

In sewing-machine work, especially in the formation of zig-zag chain stitches by the concatenation of a needle thread and an underthread, it is known to form a knot at the end of the seam by repeatedly passing the needle through the work at the same location. More particularly, after a lirst interlooping of the needle thread and the underthread, another loop is formed between these threads by a second traverse' of the needle whereupon the two loops are drawn together to form a knot as the needle thread is tensoned by the rising needle which also pulls the -knot upwardly into the work. A further descent of the needle, however, is necessary to allow the underthread-handling mechanism to draw the needle thread once more into a loop, preparatorily to an engagement of this loop by the beak of a hook associated with the thread-cutting mechanism disposed underneath the worksupporting throat plate. This third penetration of the work at the same location, as it is conventionally performed, has several disadvantages, one of them being the fact that the knot previously drawn into the work is now again pulled out at its underside which not only is unsightly but also exposes the knot to the risk of being destroyed by the cutter. Even if the cutter does not touch the knot, the reversal in the tension of the needle thread may have the effect of loosening the connection so that the threads may come apart.

Reference is made in this connection to U.S. Patent No. 777,564 (Sullivan) illustrating the conventional knottying procedure described above.

It is, therefore, the general object of my present invention to provide a means in a sewing machine for tying knots in a manner which avoids the disadvantages just described.

I have found, in accordance with this invention, that the foregoing object may be realized by a slight further displacement of the work, relative to the needle, between the second and third needle traverses, with the result that the needle thread bridges a small portion of the upper 3,478,708 Patented Nov. 18, 1969 Fice work surface and, upon being entrained by the needle on the inal penetration, pulls the knot further upwardly into the work so as not to expose it to possi-ble attack by the cutting mechanism; this operation additionally tightens the knot previously formed and affords a clean termination of the seam.

The invention will be described in greater detail with reference to the accompanying drawing in which:

FIG. 1 is a somewhat diagrammatic perspective illustration of a conventional knot-tying procedure as performed with the aid of a zig-zag sewing machine',

FIG. 2 diagrammatically illustrates, in an elevational View, the elements of a sewing machine required for carrying out the operations illustrated in FIG. 1;

FIG. 3 is a View similar to FIG. 1, illustrating the present improvement; and

FIG. 4 is a somewhat diagrammatic side-elevational view of a sewing machine, generally similar to the one disclosed in the above-identified Sullivan patent, incorporating the elements of FIG. 2.

In FIG. 1 I have shown a work 10 composed of two fabric layers 11 and 12 to be stitched together. An upper or needle thread 13 and an underthread 14 are concatenated, by a mode of stitching sometimes referred to as roll stitch, to form interlinked loops 15 which are pulled into the fabric upon the incipient formation of the next stitch. At 16 the two threads 13 and 14 have been tied into a knot resulting from the drawing together of two linkages 15 consecutively formed at the same location.

Reference will now be made to FIGS. 2 and 4 showing the work 10` supported on a movable plate 20- of a sewing machine 30 which also comprises a needle 21 on a vertically reciprocable needle holder 2.2, a presser foot 23, and conventional underthread-handling mechanism of which only a thread guide 24 has been illustrated. Also provided underneath the support plate 20 are a loop-toting hook 25 and a cutter 26.

As more particularly illustrated in FIG. 4, the sewing machine 30` comprises a cam disk 31 coupled via a worm drive 32 with the main machine shaft 33 to which the needle holder 22 is connected by way of a crank drive 34. Disk 31 is formed on one side with a pair of grooved tracks 35, 36 engaged by respective cam followers 37, 38, and on the opposite side by a track 40 engaged by a cam follower 41. The major part of grooved track 40 is of undulating shape for producing advance movements and is generally similar to the one disclosed in the aboveidentified Sullivan patent. Follower 37 is`rigid with a lever 39 which has a lixed fulcrum 42 and whose lower bifurcate end straddles a collar 43 on a pin 44 which rises from the plate 20 :supporting the Work; pin 44 is slidably guided in a slot 45 of a machine bed/46 for motion in a direction transverse to the seam, indicated by an arrow A. Plate 20 has a slot 20 (FIG. 2) to accommodate the relativelyshfting needle 21. Follower 38 is similarly mounted on la lever 47 coupled through a linkage 27 with the cutting mechanism 26.

The major part of groove 35 is of undulating shape for producing a series of zig-zag stitches, as shown in FIGS. 1 and 3, when the work is progressively advanced in a direction perpendicular to motion A (arrow B) under the control of a lever 48 carrying the cam follower 41. Lever 48 is also fulcrumed on pivot pin 42 and has a slotted extension 49 adjustably engaged by a link 50 which is coupled via a crank 51 with a shaft `52 from which a linger 53 extends to engage in a slot 54 of plate 20. With presser foot 23 bearing resiliently upon the work, the rocking of lever 48 about its fulcrum through the camming action of undulating groove 40 swings the plate 20 about pin 44 to advance the work in the direction of the seam. The drive of the needle holder 22 is so co-ordinated with the rotation of disk 31 that the needle 21 descends and penetrates the work whenever the follower 37 engages any one of the outer arcs 35a and any one of the inner arcs 35b of the undulating groove 35. At 35C the undulations are suppressed over a peripheral distance equaling the length of the two consecutive undulations, corresponding to two consecutive descents of the needle 21, this dwell being followed by an indentation 35d of reduced radial extent or depth whereby the needle moves back toward the center line of the zig-zag seam, entraining with it the trailing portion of thread 13. At a location nearly diametrically opposite the indentation 35d, groove 36 forms an indentation 36a which operates the cutter 26 to sever the threads 13 and 14.

In the normal operation of the sewing machine to produce a seam, the usual gripping and loop-spreading devices of the underthread-handling mechanism, not further illustrated, serve to interlink the threads 13 and 14 at the end of each stitch, in the manner illustrated at 15, until the end of the seam is reached. At that point the advance of the work in the direction of the seam (arrow B) is arrested by the shape of track 40 which, as shown, has an arcuate portion centered on the axis of disk 31 engaged by the follower 41 at the time the follower 37 coacts with groove section 35C. With levers 39 and 48 thus both held stationary, the needle 21 is passed a second time through the previous perforation of the Work to produce the knot 16. With the ascending needle the knot is drawn into the fabric 10, but upon a subsequent third descent at the Same location this procedure is reversed as the loop 13 formed in the needle thread 13 is engaged by the hook 25 preparatorily to the operation of the cutter 26. This reversal is due to the fact that the thread 13, in being looped around the beak of hook 25, exerts a downward pull upon the knot as the ascending branch of this loop is tensioned by the rising needle. It may happen, therefore, that the knot 16 emerges from the underside of fabric layer 12 and even enters the path of the knife 26.

In accordance with this invention, and as illustrated in FIG. 3, the third and final penetration occurs at a location 17 slightly spaced from the site of the knot 16. Thus, as indicated by arrow C, tension is exerted by the needle upon the entrained thread in such a way that knot 16 is pulled upwardly. Through a reversal of the longitudinal feed by a suitable shaping of curve 40, resulting in a backward swing of lever 48, this location 17 may lie inwardly of the seam previously formed so that the terminal portion 13" of the thread 13 extends unobtrusively, over a fraction of the length of the normal stitches, back into the seam where it is more securely held by virtue of the surrounding thread structure. Alternately, the point of final penetration may be located forwardly of the last stitch and near the centerline of the seam as indicated in dot-dash lines at 17. After the threads 13 and 14 have been cut by the knife 26, a sufficient length of thread 13 remains trailing the needle 21 for the start of a new seam.

The control and drive mechanism 31-42 illustrated in FIG. 4 is, of course, representative of a variety of equivalent arrangements well known in the art. Thus, for example, the cam disk 31 may be disposed horizontally instead of vertically, e.g. as taught in U.S. Patent No. 2,822,771 (Hale et al). Also, the longitudinal feeding of the work (direction B) may be performed by hand, rather than by the illustrated or equivalent automatic means.

I claim:

1. In a sewing machine provided with a movable work support, a vertically reciprocable needle above said support, underthread-handling means below said support, drive means for actuating said needle and Said underthread-handling means for concatenating a needle thread and an underthread, and cutting means underneath said support for severing said needle thread and underthread, the combination therewith of control means synchronized with said drive means and linked with said support for advancing a work thereon in a predetermined manner during a series of reciprocations of said needle, whereby the work is repeatedly penetrated by the needle, and for arresting said support during two consecutive penetrations of the work by the needle, whereby a knot is formed by said needle thread and underthread beneath the work, followed by a further displacement of said support in a raised position of the needle preparatorily to a nal descent thereof, with entrainment of the needle thread across a small portion of the work and upward pulling of said knot into the work by the needle during said final descent, said cutting means being coupled with said control means for severing said needle thread and underthread immediately after said final descent.

2. The combination defined in claim 1 wherein said control means comprises a rotatable camming element provided with an undulating track for a transverse displacement of said support to produce a series of zig-zag stitches, said track having a dwell extending over the length of two undulations followed by an indentation for causing said further displacement of said support.

3. The combination dened in claim Z wherein said indentation is about half as deep as any of said undulations whereby said `final descent occurs substantially along the centerline of said series of zig-zag stitches.

References Cited UNITED STATES PATENTS 777,564 12/1904 Sullivan 112-110 RICHARD I SCANLAN, IR., Primary Examiner 

